Method of making fluoropolymer dispersion

ABSTRACT

A method of making a fluoropolymer dispersion by first providing a fluoropolymer dispersion comprising fluoropolymer particles and one or more fluorinated surfactants selected from fluorinated carboxylic acids or salts thereof having the general formula:
 
[R f —O-L-COO − ] i X i+   (I)
         wherein L represents a linear fully fluorinated alkylene group, R f  represents a linear fully fluorinated aliphatic group or a linear fully fluorinated aliphatic group interrupted with one oxygen atom, X i+  represents a cation having the valence i and i is 1, 2 or 3;
 
then adding one or more non-fluorinated surfactants selected from anionic and non-ionic surfactants followed by reducing the total amount of the one or more fluorinated surfactants to an amount of not more than 500 ppm, for example not more than 250 ppm based on the total weight of the dispersion while maintaining or increasing the amount of solids in the dispersion.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional application of pending priorapplication Ser. No. 12/684,239, filed Jan. 8, 2010, now U.S. Pat. No.8,222,322; which is a continuation of application Ser. No. 11/420,386,filed May 25, 2006 and issued as U.S. Pat. No. 7,671,112; which claimspriority to Great Britain Application No. 0525978.3, filed on Dec. 21,2005; Great Britain Application No. 0523853.0, filed on Nov. 24, 2005;Great Britain Application No. 0514398.7, filed on Jul. 15, 2005; andGreat Britain Application No. 0514387.0 filed on Jul. 15, 2005; all ofwhich are herein incorporated by reference in their entirety.

The present invention relates to fluoropolymer dispersion and inparticular to a method of making fluoropolymer dispersions.

Fluoropolymers, i.e. polymers having a fluorinated backbone, have beenlong known and have been used in a variety of applications because ofseveral desirable properties such as heat resistance, chemicalresistance, weatherability, UV-stability etc. . . . The variousfluoropolymers are for example described in “Modern Fluoropolymers”,edited by John Scheirs, Wiley Science 1997. The fluoropolymers may havea partially fluorinated backbone, generally at least 40% by weightfluorinated, or a fully fluorinated backbone. Particular examples offluoropolymers include polytetrafluoroethylene (PTFE), copolymers oftetrafluoroethylene (TFE) and hexafluoropropylene (HFP) (FEP polymers),perfluoroalkoxy copolymers (PFA), ethylene-tetrafluoroethylene (ETFE)copolymers, terpolymers of tetrafluoroethylene, hexafluoropropylene andvinylidene fluoride (THV) and polyvinylidene fluoride polymers (PVDF).

The fluoropolymers may be used to coat substrates to provide desirableproperties thereto such as for example chemical resistance,weatherability, water- and oil repellency, non-stick properties etc. Forexample aqueous dispersions of fluoropolymer may be used to coat kitchenware, to impregnate fabric or textile e.g. glass fabrics, to coat paperor polymeric substrates.

A frequently used method for producing aqueous dispersions offluoropolymers involves aqueous emulsion polymerization of one or morefluorinated monomers usually followed by an upconcentration step toincrease the solids content of the raw dispersion obtained after theemulsion polymerization. The aqueous emulsion polymerization offluorinated monomers generally involves the use of a fluorinatedsurfactant. Frequently used fluorinated surfactants includeperfluorooctanoic acids and salts thereof, in particular ammoniumperfluorooctanoic acid.

Recently, perfluoroalkanoic acids having 8 or more carbon atoms, haveraised environmental concerns. For example, perfluoroalkanoic acids arenot readily biodegradable and eliminate very slowly from the body ofliving organisms, i.e. they show bioaccumulation. Accordingly, measureshave been taken to minimize the release of these compounds in theenvironment and hence methods have been developed to reduce the amountof these surfactants in aqueous dispersions and other fluoropolymerproducts.

U.S. Pat. No. 4,369,266 discloses a method whereby part of fluorinatedsurfactant is removed through ultrafiltration. WO 00/35971 furtherdiscloses a method in which the amount of fluorinated surfactant isreduced by contacting the fluoropolymer dispersion with an anionexchange resin. Other methods have been disclosed as well such as forexample removal through steam distillation as disclosed in EP 1274771. Astill further method involving decantation has been disclosed in EP 1538 177.

Generally however, a small residual amount of the fluorinated surfactantmay still remain in the aqueous dispersion with any of the methodsdescribed in the art. Depending on the effectiveness of the method, theamount may be only a few ppm or may be several hundred ppm. Hence,despite the reduced content of perfluoroalkanoic acid surfactant influoropolymer dispersion, it continues to be desirable to improve theenvironmental characteristics of these dispersions, particularly as theyare used in preparing coatings on cookware. Moreover, the methods ofreducing the content of perfluoroalkanoic acid surfactant disclosed inthe art all have the disadvantage that operators of the process may beaccidentally exposed to such compounds during the process and/orfollowing work-up procedures. Still further, some further losses of theperfluorinated alkanoic acid surfactants in these processes cannot beavoided, which presents a further potential environmental disadvantage.

It would thus be desirable to find alternative fluorinated carboxylicacids that can be used in the emulsion polymerization of fluorinatedmonomers as fluorinated surfactants and that can be recovered fromresulting aqueous dispersions using a convenient and cost effectivemethod. Desirably, the alternative fluorinated carboxylic acids showlower bio-accumulation than perfluoro alkanoic acids having 8 or morecarbon atoms, such that despite any remaining amount of the fluorinatedcarboxylic acid in the fluoropolymer dispersion, the dispersion willhave less environmental impact. Likewise, because of the lowerbio-accumulation of the alternative surfactants, the process ofrecovering them from fluoropolymer dispersion would be more advantageousfrom an environmental point of view.

In accordance with one aspect of the invention, there is provided amethod of making a fluoropolymer dispersion, the method comprising:

-   -   (i) providing a fluoropolymer dispersion comprising        fluoropolymer particles and one or more fluorinated surfactants        selected from fluorinated carboxylic acids or salts thereof        having the general formula:        [R_(f)—O-L-COO⁻]_(i)X^(i+)  (I)    -   wherein L represents a linear partially or fully fluorinated        alkylene group or an aliphatic hydrocarbon group, R_(f)        represents a linear partially or fully fluorinated aliphatic        group or a linear partially or fully fluorinated aliphatic group        interrupted with one or more oxygen atoms, X^(i+) represents a        cation having the valence i and i is 1, 2 or 3;    -   (ii) adding one or more non-fluorinated surfactants selected        from anionic and non-ionic surfactants; and    -   (iii) reducing the total amount of said one or more fluorinated        surfactants to an amount of not more than 500 ppm, for example        not more than 250 ppm based on the total weight of the        dispersion while maintaining or increasing the amount of solids        in the dispersion.

It has been found that fluorinated carboxylic acids and salts accordingto the above general formula (I) eliminate more quickly from a livingorganism, as demonstrated on rat screening studies, than perfluoroalkanoic acids having 8 or more carbon atoms. Additionally, it has beenfound that these surfactants can be used in the emulsion polymerizationof fluorinated monomers to produce fluoropolymer dispersions and can berecovered there from in an easy and convenient way. Because of theirlower bio-accumulation, the fluorinated carboxylic acids, salts andderivatives (such as ester derivatives) should provide less of anenvironmental burden in case of small losses of these compounds. Also,the process of reducing the amount of these surfactants in thedispersion should be more beneficial for operators of the process thatmay be exposed, for example accidentally, to the fluorinated carboxylicacids, their salts or derivatives used in work-up procedures followingthe recovery from the dispersion.

In a particular further aspect, the invention also provides an aqueousfluoropolymer dispersion comprising (i) fluoropolymer particles in anamount of 30 to 70% by weight, (ii) fluorinated surfactant in an amountof more than 0 ppm but not more than 500 ppm, for example not more than250 ppm, (iii) one or more non-ionic non-fluorinated surfactants and(iv) one or more anionic non-fluorinated surfactants, said fluorinatedsurfactant comprising one or more fluorinated carboxylic acids or saltsthereof corresponding to the above general formula (I).

Fluorinated Carboxylic Acids and Salts Thereof

For the sake of convenience, the term ‘fluorinated carboxylic acid’ ishereinafter used to indicate the free acid as well as salts thereof. Thefluorinated carboxylic acid used in the process of the inventioncorresponds to formula (I) above. Generally, the fluorinated carboxylicacid will be a low molecular weight compound, for example a compoundhaving a molecular weight for the anion part of the compound of not morethan 1000 g/mol, typically not more than 600 g/mol and in particularembodiments, the anion of the fluorinated carboxylic acid may have amolecular weight of not more than 500 g/mol.

Particularly preferred fluorinated carboxylic acids are those that whenadministered to rats show a recovery of at least 45%, for example atleast 50% of the administered amount after 96 hours via renalelimination and that have a renal elimination half-life of not more than35 hours, for example of not more than 30 hours in rats as testedaccording to the method set forth in the examples. Generally,fluorinated carboxylic acids in which each of the fluorinated aliphaticmoieties in the compound have not more than 3 carbon atoms fulfill theaforementioned conditions of renal recovery and half-life. Thus,preferred compounds are those in which any fluorinated alkylene groupshave not more than 3 carbon atoms and in which a fluorinated alkyl groupof the compound has not more than 3 carbon atoms.

In the above formula (I), L represents a linking group. In oneembodiment, the linking group can be a linear partially or fullyfluorinated alkylene. Fully fluorinated alkylene groups include alkylenegroups that consist of only carbon and fluorine atoms whereas partiallyfluorinated alkylene groups may additionally contain hydrogen.Generally, a partially fluorinated alkylene group should not containmore than 2 hydrogen atoms so as to be highly fluorinated and benon-telogenic or at least have minimal telogenic effects. Examples offully fluorinated alkylene groups include linear perfluorinatedalkylenes that have from 1 to 6 carbon atoms, for example linearperfluorinated alkylene groups of 1, 2, 3, 4 or 5 carbon atoms.

Examples of linear partially fluorinated alkylene groups include thosethat have from 1 to 6 carbon atoms. In a particular embodiment thelinear partially fluorinated alkylene linking group has 1, 2, 3, 4, 5 or6 carbon atoms and has only 1 or 2 hydrogen atoms. When the partiallyfluorinated alkylene group has 2 hydrogen atoms, they may be attached tothe same carbon atom or they can be attached to different carbon atoms.When they are attached to different carbon atoms, such carbon atoms canbe adjacent to each other or not. Also, in a particular embodiment, acarbon atom having 1 or 2 hydrogen atoms may be adjacent the etheroxygen atom to which the linking group is attached or adjacent thecarboxylic group to which the linking group is attached at its otherend.

In a further embodiment, the linking group L is an aliphatic hydrocarbongroup. Examples of aliphatic hydrocarbon groups include linear, branchedor cyclic aliphatic groups. Particular examples of aliphatic groupsinclude linear or branched alkylene groups of 1 to 4 carbon atoms suchas for example methylene or ethylene.

Particular examples of linking groups L may be selected from thefollowing:

—(CF₂)_(g)— wherein g is 1, 2, 3, 4, 5 or 6;

—CFH—(CF₂)_(h)— wherein h is 0, 1, 2, 3, 4 or 5;

—CF₂—CFH—(CF₂)_(d)— wherein d is 0, 1, 2, 3 or 4;

—CH₂—(CF₂)_(h)— wherein h is 1, 2, 3 or 4;

—(CH₂)_(c)— wherein c is 1, 2, 3 or 4;

In the above examples, the left side of the formula of the linking groupis the site where the linking group is connected to the ether oxygen informula (I).

The R_(f) group in formula (I) represents a linear partially or fullyfluorinated aliphatic group or a linear partially or fully fluorinatedaliphatic group interrupted with one or more oxygen atoms. In oneembodiment, R_(f) is a linear perfluorinated aliphatic group having 1 to6 carbon atoms, preferably having 1, 2, 3 or 4 carbon atoms. Accordingto another embodiment R_(f) is a linear perfluorinated aliphatic groupinterrupted with one or more oxygen atoms of which the alkylene groupsbetween oxygen atoms have not more than 4 or 6 carbon atoms, for example3 or less carbon atoms and wherein the terminal alkyl group has not morethan 4 or 6 carbon atoms, for example 3 or less carbon atoms. Accordingto a still further embodiment, R_(f) is a linear partially fluorinatedaliphatic group having 1 to 6 carbon atoms and not more than 2 hydrogenatoms or a linear partially fluorinated aliphatic group interrupted withone or more oxygen atoms and which has not more than 2 hydrogen atoms.In the latter embodiment, it will generally be preferred that anyperfluorinated alkylene moiety has not more than 4 or 6 carbon atoms andany terminal perfluorinated alkyl group, likewise preferably should nothave more than 6 carbon atoms, for example not more than 4 carbon atoms.A particular example of a partially fluorinated aliphatic group R_(f) is

CF₃CFH—.

In a particular embodiment, R_(f) may correspond to the followingformula:R_(f) ¹—[OR_(f) ²]_(p)-[OR_(f) ³]_(q)  (II)wherein R_(f) ¹ is a perfluorinated linear aliphatic group of 1 to 6carbon atoms (for example 3 or less), R_(f) ² and R_(f) ³ eachindependently represents a linear perfluorinated alkylene of 1, 2, 3 or4 carbon atoms and p and q each independently represent a value of 0 to4 and wherein the sum of p and q is at least 1.

In another embodiment, R_(f) may correspond to the following formula:R⁷ _(f)—(O)_(t)—CFH—CF₂—  (III)wherein t is 0 or 1 and R⁷ _(f) represents a linear partially or fullyfluorinated aliphatic group optionally interrupted with one or moreoxygen atoms. Typically R⁷ _(f) does not contain perfluorinatedaliphatic moieties of more than 4 or 6 carbon atoms. For example, in oneembodiment, R⁷ _(f) is a perfluorinated linear aliphatic group of 1 to 6carbon atoms. In another embodiment, R⁷ _(f) is a group corresponding toabove formula (II).

In yet a further embodiment, R_(f) may correspond to the followingformula:R_(f) ⁸—(OCF₂)_(a)—  (IV)wherein a is an integer of 1 to 6 and R_(f) ⁸ is a linear partiallyfluorinated aliphatic group or a linear fully fluorinated aliphaticgroup having 1, 2, 3 or 4 carbon atoms. When R_(f) ⁸ is a partiallyfluorinated aliphatic group, the number of carbon atoms preferably isbetween 1 and 6 and the number of hydrogen atoms in the partiallyfluorinated aliphatic groups is preferably 1 or 2.

In a still further embodiment, R_(f) may correspond to the followingformula:R_(f) ⁹—O—(CF₂)_(b)—  (V)wherein b is an integer of 1 to 6, preferably 1, 2, 3 or 4 and R_(f) ⁹is a linear partially fluorinated aliphatic group or a linear fullyfluorinated aliphatic group having 1, 2, 3 or 4 carbon atoms. When R_(f)⁹ is a partially fluorinated aliphatic group, the number of carbon atomspreferably is between 1 and 6 and the number of hydrogen atoms in thepartially fluorinated groups is preferably 1 or 2.

In a particular embodiment of the present invention, the fluorinatedcarboxylic acid corresponds to the following formula:[R_(f) ^(a)—(O)_(t)—CHF—(CF₂)_(n)—COO⁻]_(i)X^(i+)  (VI)wherein R_(f) ^(a) represents a linear partially or fully fluorinatedaliphatic group optionally interrupted with one or more oxygen atoms, tis 0 or 1 and n is 0 or 1, X^(i+) represents a cation having a valence iand i is 1, 2 or 3, with the proviso that when t is 0, the R_(f) ^(a)contains at least one ether oxygen atom.

In a particular aspect of this embodiment, the R_(f) ^(a) is selectedfrom the group consisting of linear perfluorinated aliphatic groups of 1to 6 carbon atoms, preferably having 1 to 4 carbon atoms, perfluorinatedgroups of the formula R_(f) ¹—[OR_(f) ²]_(p)-[OR_(f) ³]_(q)— whereinR_(f) ¹ is a linear perfluorinated aliphatic group of 1 to 6 carbonatoms, preferably 1 to 4 carbon atoms, R_(f) ² and R_(f) ³ eachindependently represents a linear perfluorinated alkylene of 1, 2, 3 or4 carbon atoms and p and q each independently represent a value of 0 to4 and wherein the sum of p and q is at least 1 and perfluorinated groupsof the formula R_(f) ⁴-[OR_(f) ⁵]_(k)-[OR_(f) ⁶]_(m)—O—CF₂— whereinR_(f) ⁴ is a linear perfluorinated aliphatic group of 1 to 6 carbonatoms, preferably 1 to 4 carbon atoms, R_(f) ⁵ and R_(f) ⁶ eachindependently represents a linear perfluorinated alkylene of 1, 2, 3 or4 carbon atoms and k and m each independently represent a value of 0 to4.

Fluorinated carboxylic acid of formula (VI) can be derived fromfluorinated olefins of the general formula:R^(a) _(f)—(O)_(t)—CF═CF₂  (VIa)wherein R^(a) _(f) and t are as defined above. Compounds according toformula (VIa) are well known in the art and include fluorinated olefinssuch as perfluorinated alkyl vinyl compounds, vinyl ethers in particularperfluorovinyl ethers and allyl ethers, in particular perfluorinatedallyl ethers.

Fluorinated carboxylic acids according to formula (VI) wherein n is 0can be prepared by reacting a fluorinated olefin of formula (VIa) with abase. The reaction is generally carried out in aqueous media. An organicsolvent may be added to improve the solubility of the fluorinatedolefin. Examples of organic solvents include glyme, tetrahydrofuran(THF) and acetonitrile. Additionally or alternatively a phase transfercatalyst may be used. As a base, use can be made of for example ammonia,alkali and earth alkali hydroxides. Without intending to be bound by anytheory, it is believed, that the reaction proceeds according to thefollowing sequence when ammonia is used as a base:R_(f)—(O)_(t)—CF═CF₂+NH₃+H₂O→R_(f)—(O)_(t)—CHF—COONH₄+NH₄F

The reaction is generally carried out between 0 and 200° C., for examplebetween 20-150° C. and at a pressure between about 1 bar up to about 20bar. For further purification, the obtained salts can be distilled viathe free acid or by first converting the acid into an ester derivativeand then distilling the ester derivative followed by hydrolysis of theester to obtain the purified acid or salt thereof.

Fluorinated carboxylic acids of formula (VI) wherein n is 0 can also beprepared by reacting a fluorinated olefin of formula (VIa) with ahydrocarbon alcohol in an alkaline medium and then decomposing theresulting ether in acidic conditions thereby forming the correspondingcarboxylic acid. Suitable hydrocarbon alcohols include aliphaticalcohols such as lower alkanols having 1 to 4 carbon atoms. Specificexamples include methanol, ethanol and butanol including t-butanol. Thereaction of the fluorinated olefin with the alcohol in an alkalinemedium may be carried out as described in “Furin et al., Bull KoreanChem. Soc. 20, 220 [1999]”. The reaction product of this reaction is anether derivative of the fluorinated olefin. This resulting ether can bedecomposed under acidic conditions as described in “D. C. England, J.Org. Chem. 49, 4007 (1984)” to yield the corresponding carboxylic acidor salt thereof.

To prepare fluorinated carboxylic acids of formula (VI) wherein n is 1,a free radical reaction of the fluorinated olefin of formula (VIa) withmethanol may be carried out followed by an oxidation of the resultingreaction product. The free radical reaction is typically carried outusing a free radical initiator as is typically used in a free radicalpolymerization reaction. Examples of suitable free radical initiatorsinclude persulfates such as for example ammonium persulfate. Detailedconditions of the free radical reaction of the fluorinated carboxylicacid with an alcohol can be found in “S. V. Sokolov et al., Zh. Vses.Khim Obsh 24, 656 (1979)”. The resulting alcohol derivative of thefluorinated olefin can be chemically oxidized with an oxidizing agent tothe corresponding carboxylic acid. Examples of oxidizing agents includefor example potassium permanganate, chromium (VI) oxide, RuO₄ or OsO₄optionally in the presence of NaOCl, nitric acid/iron catalyst,dinitrogen tetroxide. Typically the oxidation is carried out in acidicor basic conditions at a temperature between 10 and 100° C. In additionto chemical oxidation, electrochemical oxidation may be used as well.

In another embodiment, the fluorinated carboxylic acid corresponds tothe following formula:R_(f) ^(b)—(O)_(t)—CFH—CF₂—O—R-G  (VII)wherein R_(f) ^(b) represents a linear partially or fully fluorinatedaliphatic group optionally interrupted with one or more oxygen atoms, Ris an aliphatic hydrocarbon group, G represents a carboxylic acid orsalt thereof, t is 0 or 1. Particular examples for R include a methylenegroup or an ethylene group.

In a particular aspect of this embodiment, the R_(f) ^(b) is selectedfrom the group consisting of linear perfluorinated aliphatic groups of 1to 6 carbon atoms, preferably having 1 to 4 carbon atoms, perfluorinatedgroups of the formula R_(f) ¹—[OR_(f) ²]_(p)[OR_(f) ³]_(q)— whereinR_(f) ¹ is a linear perfluorinated aliphatic group of 1 to 6 carbonatoms, preferably 1 to 4 carbon atoms, R_(f) ² and R_(f) ³ eachindependently represents a linear perfluorinated alkylene of 1, 2, 3 or4 carbon atoms and p and q each independently represent a value of 0 to4 and wherein the sum of p and q is at least 1 and perfluorinated groupsof the formula R_(f) ⁴-[OR_(f) ⁵]_(k)-[OR_(f) ⁶]_(m)—O—CF₂— whereinR_(f) ⁴ is a linear perfluorinated aliphatic group of 1 to 6 carbonatoms, preferably 1 to 4 carbon atoms, R_(f) ⁵ and R_(f) ⁶ eachindependently represents a linear perfluorinated alkylene of 1, 2, 3 or4 carbon atoms and k and m each independently represent a value of 0 to4.

Fluorinated carboxylic acids according to formula (VII) may be preparedthrough the preparation of an intermediate of formula (VIIa):R_(f) ^(b)—(O)_(t)—CFH—CF₂—O—R—Zwherein R_(f) ^(b), t and R have the same meaning as defined above. Zrepresents a carboxylic acid ester or a carboxylamide.

The intermediate compound according to formula (VIIa) can be prepared byreacting a fluorinated olefin of the general formula (VIa) with anorganic compound of the formulaHO—R—Z  (VIIb)wherein Z and R are as defined above. Compounds according to formula(VIIb) are well known in the art and/or are commercially available. Thereaction of compound (VIa) with compound (VIIb) is typically carried outin the presence of a base although it is also possible to carry out thereaction under acidic or neutral conditions. Suitable bases includecarbonates such as potassium carbonate, sodium carbonate and lithiumcarbonate, hydroxides, alkoholates etc. The amount of base used may varywidely. For example a catalytic amount may be used. Generally the amountof base used will be about at least 1 or 2% by weight based on theamount of reactant of formula (VIIb). In a particular embodiment, theamount of base can be up to 2 times the molar amount of the reactant offormula (VIIb). The reaction is typically carried out in an aproticsolvent such as for example, tetrahydrofuran, acetonitrile, glyme,diglyme etc. Further suitable aprotic solvents are disclosed in DE3828063. The reaction is typically carried out a temperature between 0and 200° C., for example between 10 and 150° C. The reaction isgenerally carried out at an ambient pressure (1 bar) or up to 20 bar.Following the reaction, the resulting compound may be isolated andpurified by distillation.

The fluorinated carboxylic acids of formula (VII) can be readilyprepared by hydrolyzing the intermediate compound of formula (VIIa)above. In formula (VIIa) above, Z represents a carboxylic acid ester ora carboxylamide. Typically a carboxylic acid ester is used. In oneembodiment, the ester can be an aliphatic ester, e.g. an alkyl ester inwhich the number of carbon atoms in the alkyl group are from 1 to 4.Hydrolysis of the intermediate compound may be carried out under acidicor basic conditions and is generally carried out in an alcoholic acidicor basic solution of the intermediate compound. Alternatively theintermediate compound may be hydrolysed in an acidic or basic solutionof other water miscible organic solvents such as ketones, ethers etc.Typically, a basic alcoholic solution is used such as for example amethanol or ethanol solution containing an alkali metal hydroxide as thebase. Typically the hydrolysis is carried out at room temperature but itis also possible to use elevated temperatures of for example up to theboiling point of the solution.

Alternatively, the fluorinated surfactant may be prepared by reactingthe fluorinated olefin of formula (VIa) above with a hydroxy substitutedcarboxylic acid or salt thereof. Thus, in accordance with thisembodiment the fluorinated olefin of formula (VIa) is reacted with acompound of the formula:HO—R-G  (VIIc)wherein G is a carboxylic acid group or salt thereof and R is as definedabove. The reaction of a fluorinated olefin of formula (VIa) with ahydroxy compound or formula (VIIc) can be carried out under the sameconditions described above for the reaction with compounds of formula(VIIb).

In a still further embodiment, the fluorinated carboxylic acidcorresponds to one of the following formulas:R_(f) ^(c)—(OCF₂)_(u)—O—(CF₂)_(v)-AC  (VIII)wherein u is an integer of 1 to 6, v is an integer of 1 to 6, R_(f) ^(c)represents a linear perfluorinated aliphatic group of 1, 2, 3 or 4carbon atoms and AC represents a carboxylic acid group or salt thereof;andR_(f) ^(c)—O—(CF₂)_(y)—O-L¹-AC  (IX)wherein y has a value of 1, 2, 3, 4, 5 or 6, L¹ represents a linearperfluorinated alkylene of 1, 2, 3, 4, 5 or 6 carbon atoms or a linearpartially fluorinated alkylene having 1 to 6 carbon atoms and 1 or 2hydrogen atoms, R_(f) ^(c) is as defined in above formula (VIII) and ACrepresents a carboxylic acid group or salt thereof. A particular examplefor L¹ includes a group of the formula —CFH—. Particular compoundsaccording to formula (IX) include those wherein R_(f) ^(c) representsCF₃CFH—. Such groups can be obtained from decarboxylation of—CF(CF₃)COOX groups (X is a cation) in the presence of a proticsubstance as described in JOC 34, 1841 (1969).

Fluorinated carboxylic acids of formula (VIII) are commerciallyavailable from Anles Ltd., St. Petersburg, Russia. These compounds maybe prepared for example as described by Ershov and Popova in FluorineNotes 4(11), 2002. Also, these fluorinated carboxylic acids typicallyform as byproducts in the manufacturing of hexafluoropropylene oxide bydirect oxidation of hexafluoropropylene.

Fluorinated carboxylic acids according to formula (IX) can be derivedfrom reactants that are also used in the manufacturing of fluorinatedvinyl ethers as described in U.S. Pat. No. 6,255,536.

In another embodiment acid fluorides of formula (X) are reacted with ametal fluoride like KF or CsF:R_(f) ^(g)—COF  (X)wherein R_(f) ^(g) is a partially or perfluorinated linear aliphaticchain optionally interrupted with one or more oxygen atoms. Thisreaction results in an alkoxylate that can be further reacted with acarboxylic acid derivative of formula (XI)Y—(CH₂)_(n)-Q  (XI)wherein Y represents a leaving group like iodide, bromide, chloride,mesylate, tosylate and the like, n is an integer from 1 to 3, and Qrepresents a carboxyl acid group or a lower alkyl ester. The reactionresults in fluorinated carboxylic acid derivatives of formula (XII)R_(f) ^(g)—CF₂—O—(CH₂)_(n)Q  (XII)with R_(f) ^(g) n, and Q having the same meaning as above. Thecorresponding salts can be obtained by saponification.

In yet a further embodiment the fluorinated carboxylic acids correspondto formula (XIII)CF₃—CF₂—O—R_(f) ^(h)—COOX  (XIII)with R_(f) ^(h) representing a linear partially or fully fluorinatedlinear carbon chain of 1 to 8 carbon atoms optionally interrupted withone or more oxygen atoms, for example a perfluorinated linear aliphaticgroup of 1 to 6 carbon atoms, for example 1, 2, 3 or 4 carbon atoms andX is a monovalent cation. Compounds of this formula can be made byconversion of diacid difluorides of formula (XIV) in the presence ofe.g. antimony pentafluoride.FOC—CF(CF₃)—O—R_(f) ^(h)—COF  (XIV)

This conversion may be carried out at elevated temperature according tothe method described in U.S. Pat. No. 3,555,100 resulting preferably inthe decarbonylation of the secondary COF group. The resulting mono acidfluoride can be converted to the corresponding salt using well knownmethods.

Fluorinated carboxylic acids having a —O—CF₂—COOX group can be obtainedfrom the corresponding vinyl ethers —O—CF═CF₂. Reaction of the vinylether with oxygen according to U.S. Pat. No. 4,987,254 results in acidfluorides carrying a —O—CF₂COF group which can be readily converted tothe corresponding acid or salt.

Specific examples of compounds according to formula (I) include thefollowing:

R_(f)—O—CHF—COOH

-   C₃F₇—O—CHF—COOH-   CF₃—O—CF₂CF₂—CF₂—O—CHF—COOH-   CF₃CF₂CF₂—O—CF₂CF₂—CF₂—O—CHF—COOH-   CF₃—O—CF₂—CF₂—O—CHF—COOH-   CF₃—O—CF₂—O—CF₂—CF₂—O—CHF—COOH-   CF₃—(O—CF₂)₂—O—CF₂—CF₂—O—CHF—COOH-   CF₃—(O—CF₂)₃—O—CF₂—CF₂—O—CHF—COOH    R_(f)—O—CHF—CF₂—COOH-   CF₃—O—CHF—CF₂—COOH-   CF₃—O—CF₂—CF₂—O—CHF—CF₂—COOH-   CF₃—CF₂—O—CHF—CF₂—COOH-   CF₃—O—CF₂—CF₂—CF₂—O—CHF—CF₂—COOH-   CF₃—O—CF₂—O—CF₂—CF₂—O—CHF—CF₂—COOH-   CF₃—(O—CF₂)₂—O—CF₂—CF₂—O—CHF—CF₂—COOH-   CF₃—(O—CF₂)₃—O—CF₂—CF₂—O—CHF—CF₂—COOH    R_(f)—O—CF₂—CHFCOOH-   CF₃—O—CF₂—CHF—COOH-   C₃F₇—O—CF₂—CHF—COOH-   CF₃—O—CF₂—CF₂—CF₂—O—CF₂—CHF—COOH-   CF₃—O—CF₂—O—CF₂—CF₂—O—CF₂—CHF—COOH-   CF₃—(O—CF₂)₂—O—CF₂—CF₂—O—CF₂—CHF—COOH-   CF₃—(O—CF₂)₃—O—CF₂—CF₂—O—CF₂—CHF—COOH    R_(f)—O—CF₂—CHF—CF₂COOH-   CF₃—O—CF₂—CHF—CF₂—COOH-   C₂F₅—O—CF₂—CHF—CF₂—COOH-   C₃F₇—O—CF₂—CHF—CF₂—COOH-   CF₃—O—CF₂—CF₂—CF₂—O—CF₂—CHF—CF₂—COOH-   CF₃—O—CF₂—O—CF₂—CF₂—O—CF₂—CHF—CF₂—COOH-   CF₃—(O—CF₂)₂—O—CF₂—CF₂—O—CF₂—CHF—CF₂—COOH-   CF₃—(O—CF₂)₃—O—CF₂—CF₂—O—CF₂—CHF—CF₂—COOH    R_(f)—(O)_(m)—CHF—CF₂—O—(CH₂)_(n)—COOH n=1, 2 or 3; m=0 or 1-   CF₃—O—CHF—CF₂—O—CH₂—COOH-   CF₃—O—CF₂—CF₂—CF₂—O—CHF—CF₂—O—CH₂—COOH-   C₃F₇—O—CHF—CF₂—O—CH₂—COOH-   C₃F₇—O—CHF—CF₂—O—CH₂—CH₂—COOH-   C₃F₇—O—CF₂—CF₂—O—CHF—CF₂—OCH₂COOH-   C₃F₇—O—CF₂—CF₂—CF₂—O—CHF—CF₂—OCH₂COOH-   C₃F₇—O—CF₂—CHF—CF₂—OCH₂COOH-   CF₃—CHF—CF₂—O—CH₂COOH-   C₃F₇—CF₂—CHF—CF₂—OCH₂—COOH-   CF₃—O—CF₂—CF₂—O—CH₂—COOH-   CF₃—O—CF₂—CF₂—CF₂—O—CF₂—CF₂—O—CH₂—COOH-   C₃F₇—O—CF₂—CF₂—O—CH₂—COOH-   C₃F₇—O—CF₂—CF₂—O—CH₂—CH₂—COOH-   C₃F₇—O—CF₂—CF₂—O—CF₂—CF₂—OCH₂COOH-   C₃F₇—O—CF₂—CF₂—CF₂—O—CF₂—CF₂—OCH₂COOH-   C₃F₇—O—CF₂—CF₂—CF₂—OCH₂COOH-   C₄F₉—O—CH₂—COOH-   C₄F₉—O—CH₂—CH₂—COOH-   C₃F₇—O—CH₂COOH-   C₆F₁₃—OCH₂—COOH    R_(f)—O—CF₂—CF₂—COOH-   CF₃—O—CF₂—CF₂—COOH-   C₂F₅—O—CF₂—CF₂—COOH-   C₃F₇—O—CF₂—CF₂—COOH-   C₄F₉—O—CF₂—CF₂—COOH    R_(f)—(O—CF₂)_(u)—O—CF₂—COOH with u being as Defined Above-   CF₃—(O—CF₂)₃—O—CF₂—COOH-   CF₃—(O—CF₂)₂—O—CF₂—COOH-   CF₃—(O—CF₂)₁—O—CF₂—COOH    R_(f)—(O—CF₂—CF₂)_(k)—O—CF₂—COOH with k being 1, 2 or 3-   CF₃—(O—CF₂—CF₂)₁—O—CF₂—COOH-   C₂F₅—(O—CF₂—CF₂)₁—O—CF₂—COOH-   C₃F₇—(O—CF₂—CF₂)₁—O—CF₂—COOH-   C₄F₉—(O—CF₂—CF₂)₁—O—CF₂—COOH-   C₂F₅—(O—CF₂—CF₂)₂—O—CF₂—COOH-   CF₃—(O—CF₂—CF₂)₂—O—CF₂—COOH-   C₃F₇—(O—CF₂—CF₂)₂—O—CF₂—COOH-   C₄F₉—(O—CF₂—CF₂)₂—O—CF₂—COOH    R_(f)—O—CF₂—COOH-   C₃F₇—O—CF₂—COOH-   CF₃—O—CF₂—CF₂—CF₂—O—CF₂—COOH    CF₃—CHF—O—(CF₂)_(n)—COOH with o being an Integer of 1, 2, 3, 4, 5 or    6-   CF₃CFH—O—(CF₂)₃—COOH-   CF₃CFH—O—(CF₂)₅—COOH    CF₃—CF₂—O—(CF₂)_(n)—COOH with o being as Above-   CF₃—CF₂—O—(CF₂)₃COOH-   CF₃—CF₂—O—(CF₂)₅COOH

In the above generic formulas, R_(f) has the meaning as defined above inrespect of generic formula (I). It is understood that while the abovelist of compounds only lists the acids, the corresponding salts, inparticular the NH₄ ⁺, potassium, sodium or lithium salts can equally beused.

Non-Ionic Non-Fluorinated Surfactants

Suitable non-fluorinated non-ionic surfactants include those describedin “Nonionic Surfactants”, M. J. Schick (ed.), Marcel Dekker, Inc., NewYork 1967. Examples of non-ionic surfactants can be selected from thegroup of alkylarylpolyethoxy alcohols, polyoxyalkylene alkyl ethersurfactants, polysorbates and alkoxylated acetylenic diols, preferablyethoxylated acetylenic diols and mixtures of such surfactants.Preferably, the non-ionic surfactant or non-ionic surfactant mixtureused will have an HLB (hydrophilic lypophilic balance) between 11 and16. The HLB number was introduced by W. C. Griffin “Calculation of HLBValues of Non-Ionic Surfactants,” Journal of the Society of CosmeticChemists 5 (1954), p. 259 to characterize surfactants. The HLB number ofnon-ionic surfactants having only ethyleneoxide groups can be calculatedaccording to the formula HLB=E/5 where E represents the weight % ofethyleneoxide groups. In case of a mixture of surfactants, the HLB valuecan be calculated according to the formula:

${HLB} = {\sum\limits_{i = 0}^{n}\;{{HLBi}*{{wi}.}}}$wherein HLB_(i) represents the HLB of surfactant i and w_(i) representsthe weight fraction of surfactant i in the surfactant mixture and nrepresents the number of different surfactants making up the surfactantmixture.

In one embodiment, the non-ionic surfactant or mixture of non-ionicsurfactants corresponds to the general formula:R¹—O—[CH₂CH₂O]_(n)—[R²O]_(m)—R³  (XV)wherein R¹ represents a linear or branched aliphatic or aromatichydrocarbon group having at least 8 carbon atoms, preferably 8 to 18carbon atoms, R² represents an alkylene having 3 carbon atoms, R³represents hydrogen or a C₁-C₃ alkyl group, n has a value of 0 to 40, mhas a value of 0 to 40 and the sum of n+m is at least 2. When the abovegeneral formula represents a mixture, n and m will represent the averageamount of the respective groups. Also, when the above formula representsa mixture, the indicated amount of carbon atoms in the aliphatic groupR¹ may be an average number representing the average length of thehydrocarbon group in the surfactant mixture. Commercially availablenon-ionic surfactant or mixtures of non-ionic surfactants include thoseavailable from Clariant GmbH under the brand GENAPOL™ such as GENAPOL™X-080, a surfactant according to the above formula (XV) in which m is 0and GENAPOL™ PF 40 a surfactant in which both n and m are non-zero.Further suitable non-ionic surfactants that are commercially availableinclude Tergitol™ TMN 6 or Tergitol™ TMN 100X, Tergitol™ TMN 10, andTriton® X-100.

According to a further embodiment, a mixture of one or more surfactantsaccording to formula (XV) in which m is 0 with one or more surfactantsaccording to formula (XV) with n and m each being non-zero can be used.An example of such a mixture is a mixture of GENAPOL™ X-080 and GENAPOL™PF40.

In a still further embodiment, one or more polysorbates may be usedoptionally in combination with one or more surfactants according toformula (XV). Polysorbates are ethoxylated sorbitan fatty esters and arewell known as emulsifiers. Useful polysorbates include polysorbate 20,polysorbate 40, polysorbate 60 and polysorbate 80. The structure ofpolysorbate 80 is disclosed in e.g. EP 1452571.

Polysorbate 20, 40 and 60 have a very similar structure as polysorbate80. Polysorbate 20, is a laurate ester of sorbitol and its anhydrideshaving approximately twenty moles of ethylene oxide for each mole ofsorbitol and sorbitol anhydrides. Polysorbate 40 is a palmitate ester ofsorbitol and its anhydrides having approximately twenty moles ofethylene oxide for each mole of sorbitol and sorbitol anhydrides.Polysorbate 60 is a mixture of stearate and palmitate esters of sorbitoland its anhydrides having approximately twenty moles of ethylene oxidefor each mole of sorbitol and sorbitol anhydrides.

Further non-ionic surfactants that can be used include alkoxylatedacetylenic diols, for example ethoxylated acetylenic diols. Theethoxylated acetylenic diols for use in this embodiment preferably havea HLB between 11 and 16. Commercially available ethoxylated acetylenicdiols that may be used include those available under the SURFYNOL brandfrom Air Products, in particular SURFYNOL™ 465. Still further usefulnon-ionic surfactants include polysiloxane based surfactants such asSilwet® L77 commercially available from Crompton Corp.

Anionic Non-Fluorinated Surfactants

Anionic non-fluorinated surfactants that may be used in connection withthis invention include surfactants that have an acid group, inparticular a sulfonic or carboxylic acid group. Examples ofnon-fluorinated anionic surfactants include surfactants that have one ormore anionic groups. Anionic non-fluorinated surfactants may include inaddition to one or more anionic groups also other hydrophilic groupssuch as polyoxyalkylene groups having 2 to 4 carbons in the oxyalkylenegroup, such as polyoxyethylene groups. Typical non-fluorinatedsurfactants include anionic hydrocarbon surfactants. The term “anionichydrocarbon surfactants” as used herein comprises surfactants thatcomprise one or more hydrocarbon moieties in the molecule and one ormore anionic groups, in particular acid groups such as sulfonic,sulfuric, phosphoric and carboxylic acid groups and salts thereof.Examples of hydrocarbon moieties of the anionic hydrocarbon surfactantsinclude saturated and unsaturated aliphatic groups having for example 6to 40 carbon atoms, preferably 8 to 20 carbon atoms. Such aliphaticgroups may be linear or branched and may contain cyclic structures. Thehydrocarbon moiety may also be aromatic or contain aromatic groups.Additionally, the hydrocarbon moiety may contain one or more heteroatoms such as for example oxygen, nitrogen and sulfur.

Particular examples of anionic hydrocarbon surfactants for use in thisinvention include alkyl sulfonates such as lauryl sulfonate, alkylsulfates such as lauryl sulfate, alkylarylsulfonates andalkylarylsulfates, fatty (carboxylic) acids and salts thereof such aslauric acids and salts thereof and phosphoric acid alkyl or alkylarylesters and salts thereof. Commercially available anionic hydrocarbonsurfactants that can be used include Polystep™ A16 (sodium dodecylbenzylsulphonate) from Stepan Company, Hostapur™SAS 30 (secondary alkylsulphonate sodium salt), Emulsogen™ LS (sodium lauryl sulfate) andEmulsogen™ EPA 1954 (mixture of C₁₂ to C₁₄ sodium alkyl sulfates)available from Clariant GmbH, Edenor C-12 (Laurie acid) available fromCognis and TRITON™ X-200 (sodium alkylsulfonate) available from UnionCarbide. Further suitable anionic surfactants include thesulfosuccinates disclosed in EP 1538177 and EP 1526142. Preferred areanionic hydrocarbon surfactants having a carboxylic acid group.

In a particular embodiment in connection with the present invention, acombination of non-ionic surfactants and anionic hydrocarbon surfactantsis selected such that the Viscosity Transition Temperature (VTT) of thedispersion is at least 26° C., preferably at least 28° C. Suitablemixtures to achieve a VTT of at least 26° C. have been disclosed in EP1452571.

Reducing the Amount of Fluorinated Surfactant in the FluoropolymerDispersion

In accordance with the method of the invention, the amount offluorinated surfactant is reduced to a level of not more than 500 ppm ormore than 250 ppm while maintaining or increasing the amount of solidsin the dispersion. To avoid coagulation of the dispersion while reducingthe amount of fluorinated surfactant, a non-ionic and/or anionicnon-fluorinated surfactant is added to the dispersion. Depending on theparticular method for reducing the fluorinated surfactant, a non-ionicand/or anionic surfactant can be used as the stabilizing surfactant.Generally, a non-ionic surfactant can be used in any of the methods ofreducing the amount of fluorinated surfactant in the dispersion whereasthe utility of anionic surfactants is more limited.

The removal of fluorinated surfactant is preferably carried out usingcrude or raw dispersions directly from the polymerization of fluorinatedmonomers. Crude dispersions typically have a solids content of 10 to 40%by weight. Nonionic and/or anionic emulsifiers are typically added tothe crude dispersions in amount sufficient to provide a desireddispersion stability after reduction of the fluorinated surfactant. Anamount from 0.5 to 20% by weight, preferably from 1 to 12% by weight ofnon-ionic/anionic emulsifier is generally sufficient for this purpose.Although reducing the amount of fluorinated surfactant in the crudedispersion is generally preferred, it is also possible to reduce theamount of fluorinated surfactant while upconcentrating the dispersion orafter upconcentration of the dispersion. If an upconcentrated dispersionis used, the amount of solids may be between 40 and 70% by weight, forexample between 45 and 65% by weight. Hence, the fluorinated surfactantmay be reduced in dispersions having a solids content of 10 to 70% byweight, for example between 15 and 65% by weight.

Suitable methods for reducing the fluorinated surfactant content in thedispersion include contacting the aqueous dispersion with an anionexchange resin, ultrafiltration as disclosed in e.g. U.S. Pat. No.4,369,266, a method involving decantation as disclosed in EP 1 538 177and a method involving steam distilling the free acid form of thefluorinated surfactant as disclosed in EP 1274771.

In one particular embodiment for reducing the amount of fluorinatedsurfactant, a non-ionic non-fluorinated surfactant is added to theaqueous dispersion and the so obtained dispersion is contacted with ananion exchange resin. In a particular embodiment, the anion exchangeprocess is carried out in essentially basic conditions. Accordingly, theion exchange resin will preferably be in the OH⁻ form although anionslike fluoride or oxalate corresponding to weak acids may be used aswell. The specific basicity of the ion exchange resin is not verycritical. Strongly basic resins are preferred because of their higherefficiency in removing the low molecular weight fluorinated surfactant.The process may be carried out by feeding the fluoropolymer dispersionthrough a column that contains the ion exchange resin or alternatively,the fluoropolymer dispersion may be stirred with the ion exchange resinand the fluoropolymer dispersion may thereafter be isolated byfiltration. With this method, the amount of fluorinated surfactant canbe reduced to levels below 150 ppm or even below 10 ppm. Accordingly,dispersions substantially free of fluorinated surfactant may thereby beobtained. Additionally, the anion exchange resin will typically alsoremove other low molecular weight fluorinated substances that have ananionic group.

In another embodiment, the amount of fluorinated surfactant may bereduced by ultrafiltration. The method of ultrafiltration comprises thesteps of (a) adding non-ionic and/or anionic non-fluorinated surfactantto a dispersion and (b) circulating the dispersion over a semi-permeableultra-filtration membrane to separate the dispersion into a fluorinatedpolymer dispersion and an aqueous permeate. The circulation is typicallyat a conveying rate of 2 to 7 meters per second and affected by pumps,which keep the fluorinated polymer free from contact with componentswhich cause frictional forces. The method of ultrafiltration further hasthe advantage that during ultrafiltration the amount of fluorinatedsurfactant can be reduced while at the same time increasing the solidsin the dispersion, i.e. upconcentrating the dispersion. If theultrafiltration is to be used solely for reducing the level offluorinated surfactant in the dispersion without increasing the amountof solids, water may be added to the dispersion during theultrafiltration in amounts so as to maintain the amount of solids in thedispersion constant.

In a still further embodiment, the amount of fluorinated surfactant maybe reduced in the dispersion through distillation of the free acid formof the surfactant. This process can be used if the surfactant in itsfree acid form is steam volatile, which is typically the case for thefluorinated carboxylic acids of formula (I). Typically, this methodinvolves adding a non-ionic and/or anionic emulsifier to the aqueousfluoropolymer dispersion and removing steam-volatile fluorinatedemulsifier by distillation until the concentration of steam-volatilefluorinated emulsifier in the dispersion reaches the desired value.Generally, the method is practiced at a low pH, for example a pH of 5 orless. The low pH can be produced by adding customary strong mineralacids, such as HCl, H₂SO₄, HClO₄, or HNO₃. HNO₃ is preferred, since theNH₄NO₃ that may be formed in a subsequent neutralization of thedispersion with NH₃ is noncorrosive, has adequate volatility and doesnot interfere with the sintering of the fluoropolymer. A cation-exchangeprocess, as described in

U.S. Pat. No. 5,463,021 for example, is also suitable for setting thedesired pH and for preparing particularly pure dispersions.

Further methods that can be used to reduce the amount of fluorinatedcarboxylic acid in the dispersion include decantation methods asdisclosed in for example EP 1538177 and EP 1526142. If desired, theconductivity of the dispersion may be adjusted subsequent to thereduction of the amount of fluorinated carboxylic acid. Generally, theconductivity of the dispersion should be at least 50 μS/cm, usually 100μS/cm or higher, limited by the viscosity of the dispersion.

Fluoropolymer Dispersions

The fluoropolymer contained in the fluoropolymer dispersion is a polymerthat has a partially or fully fluorinated backbone. Typically thefluoropolymer is a polymer that has a backbone that is at least 40% byweight fluorinated, preferably at least 50% by weight, more preferablyat least 60% by weight. The fluoropolymer may also have a fullyfluorinated backbone such as for example in PTFE. The fluoropolymercontained in the aqueous dispersion includes melt-processible as well asnon-melt processible fluoropolymers. By the term melt-processible ismeant a fluoropolymer that has a melt flow index (MFI) sufficientlylarge such that the polymer can be processed with available polymer meltprocessing equipment. Examples of non-melt processible fluoropolymersinclude polytetrafluoroethylene (PTFE) and so-called modified PTFE,which is a polymer of tetrafluoroethylene modified with minor amounts,e.g. 1% or less, of another fluorinated monomer such as for example aperfluorinated vinyl ether. Melt-processible fluoropolymers include theso-called fluorothermoplasts and fluoropolymers for the preparation offluoroelastomers. Fluorothermoplasts typically have a well defined andpronounced melting point. Typically, the melting point of afluorothermoplast will be at least 60° C. with a preferred range beingbetween 100° C. and 320° C. The fluoropolymer of the fluoropolymerdispersion may also be a polymer that upon curing results in afluoroelastomer. Typically, such fluoropolymers are amorphousfluoropolymers that have no melting point or that have a hardlynoticeable melting point. Still further, the fluoropolymer may compriseso-called micro-powder, which is typically a low molecular weightpolytetrafluoroethylene. Due to the low molecular weight of the PTFE,micro-powders are melt processible.

The fluoropolymer dispersions for use in this invention may be producedby aqueous emulsion polymerization of one or more fluorinated monomersusing one or more fluorinated carboxylic acids according to formula (I)as emulsifiers or fluorinated surfactants. Typically the amount offluorinated surfactant used will be between 0.001 and 1% by weight.Examples of fluorinated monomers that may be polymerized with thefluorinated carboxylic acids of formula (I) include partially or fullyfluorinated gaseous monomers including fluorinated olefins such astetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, vinylfluoride, vinylidene fluoride, partially or fully fluorinated allylethers and partially or fully fluorinated vinyl ethers. Thepolymerization may further involve non-fluorinated monomers such asethylene and propylene.

Further examples of fluorinated monomers that may be used in the aqueousemulsion polymerization according to the invention include thosecorresponding to the formula:CF₂═CF—O—R_(f)wherein R_(f) represents a perfluorinated aliphatic group that maycontain one or more oxygen atoms. Preferably, the perfluorovinyl etherscorrespond to the general formula:CF₂═CFO(R_(f)—O)_(n)(R′_(f)—O)_(m)R″_(f)wherein R_(f) and R′_(f) are different linear or branchedperfluoroalkylene groups of 2-6 carbon atoms, m and n are independently0-10, and R″_(f) is a perfluoroalkyl group of 1-6 carbon atoms. Examplesof perfluorovinyl ethers according to the above formulas includeperfluoro-2-propoxypropylvinyl ether (PPVE-2),perfluoro-3-methoxy-n-propylvinyl ether, perfluoro-2-methoxy-ethylvinylether, perfluoromethylvinyl ether (PMVE), perfluoro-n-propylvinyl ether(PPVE-1) andCF₃—(CF₂)₂—O—CF(CF₃)—CF₂—O—CF(CF₃)—CF₂—O—CF═CF₂.

Still further, the polymerization may involve comonomers that have afunctional group such as for example a group capable of participating ina peroxide cure reaction. Such functional groups include halogens suchas Br or I as well as nitrile groups. Specific examples of suchcomonomers that may be listed here include

-   -   (a) bromo- or iodo-(per)fluoroalkyl-(per)fluorovinylethers        having the formula:        Z—R_(f)—O—CX═CX₂        wherein each X may be the same or different and represents H or        F, Z is Br or I, R_(f) is a (per)fluoroalkylene C₁-C₁₂,        optionally containing chlorine and/or ether oxygen atoms; for        example: BrCF₂—O—CF═CF₂, BrCF₂CF₂—O—CF═CF₂,        BrCF₂CF₂CF₂—O—CF═CF₂, CF₃CFBrCF₂—O—CF═CF₂, and the like; and    -   (b) bromo- or iodo containing fluoroolefins such as those having        the formula:        Z′—(R_(f)′)_(r)—CX═CX₂,        wherein each X independently represents H or F, Z′ is Br or I,        R_(f)′ is a perfluoroalkylene C₁-C₁₂, optionally containing        chlorine atoms and r is 0 or 1; for instance:        bromotrifluoroethylene, 4-bromo-perfluorobutene-1, and the like;        or bromofluoroolefins such as 1-bromo-2,2-difluoroethylene and        4-bromo-3,3,4,4-tetrafluorobutene-1.

Examples of nitrile containing monomers that may be used include thosethat correspond to one of the following formulas:CF₂═CF—CF₂—O—R_(f)—CNCF₂═CFO(CF₂)_(w)CNCF₂═CFO[CF₂CF(CF₃)O]_(g)(CF₂)_(v)OCF(CF₃)CNCF₂═CF[OCF₂CF(CF₃)]_(k)O(CF₂)_(u)CNwherein w represents an integer of 2 to 12; g represents an integer of 0to 4; k represents 1 or 2; v represents an integer of 0 to 6; urepresents an integer of 1 to 6, R_(f) is a perfluoroalkylene or abivalent perfluoroether group. Specific examples of nitrile containingliquid fluorinated monomers includeperfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene), CF₂═CFO(CF₂)₅CN, andCF₂═CFO(CF₂)₃OCF(CF₃)CN.

Examples of fluoropolymers of the fluoropolymer dispersion include PTFE,modified PTFE, micro-powder, a copolymer of vinylidene fluoride andhexafluoropropylene, a copolymer of tetrafluoroethylene and vinylidenefluoride, a copolymer of tetrafluoroethylene and propylene, a copolymerof tetrafluoroethylene and perfluorovinyl ether, a copolymer ofvinylidene fluoride and perfluorovinyl ether, a copolymer oftetrafluoroethylene, ethylene or propylene and perfluorovinyl ether, acopolymer of tetrafluoroethylene, hexafluoropropylene andperfluorovinylether, a copolymer of tetrafluoroethylene, vinylidenefluoride and hexafluoropropylene and optionally chlorotrifluoroethylene(CTFE), a copolymer of vinylidene fluoride, tetrafluoroethylene andperfluorovinyl ether and a copolymer of tetrafluoroethylene, ethylene orpropylene, hexafluoropropylene and perfluorovinyl ether. Furtherexamples of fluoropolymers include copolymers of tetrafluoroethylenewhich can be processed from the melt, especially those oftetrafluoroethylene/hexafluoropropylene,tetrafluoroethylene/perfluoro(alkylvinyl)ethers with perfluoroalkylradicals having 1 to 5 C atoms, in particularperfluoro(n-propyl-vinyl)ethers, tetrafluoroethylene/ethylene,tetrafluoroethylene/trifluorochloroethylene,trifluorochloroethylene/ethylene, tetrafluoroethylene/vinylidenefluoride and hexafluoropropylene/vinylidene fluoride, and terpolymers oftetrafluoroethylene/perfluoro(alkylvinyl)ether/hexafluoropropylene,tetrafluoroethylene/ethylene/hexafluoropropylene andtetrafluoroethylene/vinylidene fluoride/hexafluoropropylene, or ofquaternary polymers of tetrafluoroethylene/vinylidenefluoride/hexafluoropropylene/perfluoro(alkylvinyl)ethers andtetrafluoroethylene/ethylene/hexafluoropropylene/perfluoro(alkylvinyl)ethers.Further fluoropolymers that can be used in the dispersion includepolyvinyl fluoride, polyvinylidene fluoride andpolytrifluorochloroethylene.

The particle size of the fluoropolymer in the aqueous fluoropolymerdispersion is typically between 40 nm and 400 nm as such particle sizes(Z average particle diameter) typically result from an emulsionpolymerization. Smaller particle sizes are contemplated as well, forexample between 30 nm and 60 nm, which are typically obtained withmicroemulsion polymerization. Generally, after polymerization theparticles will be spherical but rod shaped particles may be obtained aswell and/or may be present in admixture with spherical particles.

In a particular embodiment in connection with this invention, a mixtureof fluoropolymer particles is used that have a distinct average particlesize such that the mixture has a bimodal or multi-modal distribution inparticle size. For example, in one embodiment, a mixture offluoropolymer particles having an average particle size of not more than100 nm, for example between 30 and 90 nm or between 50 and 80 nm, ismixed with fluoropolymer particles having an average particle size of atleast 180 nm, for example 190 nm to 400 nm or 200 nm to 350 nm. Thefluoropolymer particles having distinct average particle sizes may be ofthe same or similar chemical composition or they can be different. Forexample, in one embodiment the mixture may comprise non-melt processiblefluoropolymer particles of distinct average particle diameter. Inanother embodiment, a mixture of a melt-processible and non-meltprocessible fluoropolymer or of two melt processible fluoropolymers withdifferent particle sizes may be used.

In a particular embodiment in connection with the present invention,there is provided an aqueous fluoropolymer dispersion comprising (i)fluoropolymer particles in an amount of 30 to 70% by weight, (ii)fluorinated surfactant in an amount of more than 0 ppm but not more than500 ppm, or not more than 250 ppm or not more than 100 ppm, (iii) one ormore non-ionic non-fluorinated surfactants and (iv) one or more anionicnon-fluorinated surfactants, whereby the fluorinated surfactantcomprises one or more fluorinated carboxylic acids or salts thereofhaving the general formula (I) defined above.

Dispersions according to this embodiment may provide in particular theadvantage of improved stability and generally have desirable viscosityproperties which is an advantage in coating applications, in particular,such dispersion will generally have a constant viscosity over a certaintemperature range. In a particular aspect of this embodiment, thefluoropolymer is selected from homo- or copolymers oftetrafluoroethylene (TFE) including such polymers of TFE that are meltprocessible or not. In a preferred aspect of this embodiment, thenon-ionic non-fluorinated surfactants do not comprise aromatic groupcontaining surfactants. Also, the anionic surfactant in this embodimentis preferably a carboxylic fatty acid such as lauric acid. Typically theamount of non-ionic non-fluorinated surfactant in the dispersion isbetween 1 and 15% by weight (based on solids in the dispersion) and theamount of anionic non-fluorinated surfactant is typically between 10 ppmand 5000 ppm, preferably between 100 ppm and 3000 ppm, more preferablybetween 100 ppm and 2500 ppm based on the weight of the fluoropolymersolids in the dispersion.

The dispersions prepared in accordance with the present invention may beused in any application in which aqueous fluoropolymer dispersions aretypically used. Such applications include in particular the coating ofsubstrates such as metal substrates including aluminium substrates andstainless steel for cook and bakeware and technical applications andglass fabrics as well as impregnation applications. The dispersion mayalso be used in polymer additive applications.

EXAMPLES Test Method

Content of Fluorinated Carboxylic Acid

The amount of fluorinated carboxylic acid in aqueous solution wasdetermined by conversion of the fluorinated emulsifier into the methylester followed by an analysis with gas chromatography (head space) usingmethyl ester of perfluorodecanoic acid as an internal standard. Thedetection limit was about 10 ppm.

Particle Size

The latex particle size determination was conducted by means of dynamiclight scattering with a Malvern Zetazizer 1000 HAS in accordance toISO/DIS 13321. Prior to the measurements, the polymer lattices asyielded from the polymerizations were diluted with 0.001 mol/LKCl-solution, the measurement temperature was 25° C. in all cases. Thereported average is the Z-average particle diameter.

-   SSG: Standard specific gravity was measured according ASTM 4894-04-   Solid Content for raw dispersions: Determination of solid content    was done by subjecting the latex sample to a temperature up to    250° C. for 30 min.-   Solid Content for concentrated dispersions: Determination of solid    content was done according to ISO 12086 (2 h 120° C., 35 min 380°    C.).    Polymerization of Fluorinated Monomers (Fluoroolefin) Using a    Fluorinated Carboxylic Acid

The polymerization experiments were performed in a 40 l kettle equippedwith an impeller agitator and a baffle. The kettle was charged with 30 lof deionized water and set to 35° C.; the kettle was evacuatedrepeatedly to remove oxygen; Agitation speed was set to 165 rpm. Theoxygen free kettle was charged with 70 mmol fluorinated emulsifier(unless specified differently) as listed in table 3 and the followingmaterials were added: 0.5 ml of a solution containing 40 mg of coppersulphate penta hydrate and 1 mg of conc. sulphuric acid; 15 g of a 25w-% of aqueous ammonia solution and 5.6 g ofCF₃CF₂CF₂—O—CF(CF₃)—CF₂—O—CF═CF₂ (PPVE-2). Finally the reactor waspressurized with tetrafluoroethylene (TFE) to 0.2 MPa and 47 g ofhexafluoropropylene (HFP) were added. The kettle was then set to 1.5 MPausing TFE and 100 ml of an aqueous initiator solution containing 140 mgof sodium disulfite followed by 100 ml of a solution containing 340 mgof ammonium peroxodisulfate was pumped into the reactor. The beginningof the polymerization is indicated by a pressure drop. Duringpolymerization the pressure was maintained at 1.5 MPa by feeding TFEcontinuously. After 3.2 kg of TFE had been added, the monomer valve wasclosed and the pressure was released. The characteristics of theobtained polymer lattices are summarized in table 3.

1000 ml of this polymer dispersion were coagulated by adding 20 mlhydrochloric acid under agitation. The coagulated material wasagglomerated with gasoline and washed repeatedly. The agglomeratedpolymer was dried overnight at 200° C. in a vacuum oven; test data aregiven in table 3.

TABLE 1 Emulsifiers used: C₇F₁₅COONH₄ Comparative example C-1

Comparative example C-2

Comparative example C-3 CF₃—O—(CF₂)₃—O—CF₂—COONH₄ Compound 1CF₃—OCF₂—O—CF₂—COONH₄ Compound 2 CF₃—OCF₂—OCF₂—OCF₂—COONH₄ Compound 3CF₃—(OCF₂)₃—OCF₂—COONH₄ Compound 4 C₃F₇—O—CF₂—COONH₄ Compound 5CF₃—O—CF₂—CF₂—COONH₄ Compound 6 C₂F₅—O—CF₂—CF₂—COONH₄ Compound 7C₃F₇—O—CF₂—CF₂—COONH₄ Compound 8 C₄F₉—O—CF₂—CF₂—COONH₄ Compound 9C₂F₅—O—CF₂—CF₂—O—CF₂—COONH₄ Compound 10CF₃—O—CF₂—CF₂—CF₂—O—CHF—CF₂—COONH₄ Compound 11CF₃—O—CF₂—CF₂—CF₂—O—CHF—COONH₄ Compound 12 C₃F₇—O—CFH—CF₂COONH₄ Compound13 CF₃—CFH—O—(CF₂)₅—COONH₄ Compound 14 CF₃—CFH—O—(CF₂)₃—COONH₄ Compound15 C₃F₇—O—CFH—CF₂—O—CH₂—COONH₄ Compound 16 C₃F₇—O—CFH—COONH₄ Compound 17

Preparation of Compound 1: CF₃OCF₂CF₂CF₂OCF₂COONH₄

Oxidation of perfluorinated vinyl ethers with oxygen in the presence ofSbF₅ was carried out as described in U.S. Pat. No. 4,987,254. Theinitially formed acid fluorides were esterified with methanol andpurified by distillation. The distilled esters were converted to thecorresponding ammonium salts by saponification with aqueous ammonia. Adry flask equipped with a magnetic stirrer bar, thermometer, dry icereflux condenser, dropping funnel, and gas inlet tube was charged with 5g of graphite. The flask was flushed with nitrogen and 332 g ofCF₃OCF₂CF₂CF₂OCF═CF₂ were added at room temperature. 2.6 g of SbF₅ wasadded via the dropping funnel and oxygen was charged to the flask atambient pressure. An exothermic reaction indicated the oxidation. Totalreaction time was 14 h. After the first hour 2.6 g and after 7 hours 3.5g of SbF₅ were added. Esterification was achieved by slow addition of 50g of methanol to the reaction mixture. The resulting ester was isolatedfrom the batch by flash distillation after addition of 300 g water and50 g methanol. The distillate formed two phases. The lower phase wasseparated and the upper phase returned to the flask. 310 g of lowerphase were collected. GC analysis showed a content of 52% ofCF₃OCF₂CF₂CF₂OCF₂COOCH₃. Purification via fractionated distillationresulted in 144 pure ester with a boiling point of 51° C. at 52 mbar.CF₃OCF₂CF₂COOCH₃ was isolated as by product. Saponification of the esterwith aqueous ammonia at 60-80° C. and removal of methanol bydistillation resulted in an aqueous solution of CF₃OCF₂CF₂CF₂OCF₂COONH₄.All structures were confirmed by F-NMR spectra.

Preparation of Compound 5: CF₃CF₂CF₂OCF₂COONH₄

Using the procedures described in U.S. Pat. No. 4,987,254,CF₃CF₂CF₂OCF═CF₂ was converted to CF₃CF₂CF₂OCF₂COOCH₃ (bp 102-104° C.).Saponification with aqueous ammonia and removal of methanol bydistillation resulted in an aqueous solution of CF₃CF₂CF₂OCF₂COONH₄.Structures were confirmed by F-NMR spectra.

Preparation of Compound 17: CF₃CF₂CF₂OCHFCOONH₄

A 2 liter glass flask equipped with a mechanical stirrer, thermometerand reflux condenser (−80° C.) is used. Heating of the flask is providedby an electric heating mantle. The conversion is carried out as a onepot reaction. 275 g perfluoropropyl vinyl ether (PPVE), 280 g KOH, 602 gwater, 151 g t-butanol, and 10 g methyl trioctyl ammonium chloride areplaced in the flask. The three phase mixture is subjected to vigorousstirring. After initial heating a moderate exothermic reaction occurs.Mixing is continued for nine hours. During this time the internaltemperature adjusts to 27-33° C. Mixing is stopped when the exothermicreaction ceases. The reaction mixture forms two layers. The lowtemperature reflux condenser is replaced by a standard reflux condenser.Sulfuric acid (392 g) is slowly added without external cooling. Thebatch is heated to reflux. Unreacted PPVE is vented. At about 80° C.internal temperature gas begins to evolve. Heating is continued untilthe gas evolution has ceased. At this time the internal temperaturereaches 101° C. The batch is cooled to RT and the reflux condenser isreplaced by a distillation device. No column is used. 110 g methanol isadded to the batch and distillation is started. The condensed vaporsform two layers. The lower layer is separated and the upper layer isreturned to the flask. Distillation is stopped when no more lower phaseis formed. In total, 234 g of lower phase are collected. Fractionationof the lower phase yields 167 g of C₃F₇OCHFCOOCH₃ with a boiling pointof 120-122° C. at ambient pressure. Calculated yield: 59% based on totalPPVE used; 70% based on converted PPVE. The ester is converted to theammonium salt by reaction with aqueous ammonia. Methanol is removed byfractionated distillation. The resulting aqueous solution is used as anemulsifier in the polymerization of fluorinated olefins.

Preparation of Compound 12: CF₃OCF₂CF₂CF₂OCHFCOONH₄

A glass flask equipped with a reflux condenser, thermometer, andmagnetic stirrer was used. Perfluoromethoxy propyl vinyl ether (498 g),t-butanol (149 g), water (1007 g), potassium hydroxide (280 g), andmethyl trioctyl ammonium chloride (10 g) were added to the flask. Theresulting two phase mixture was heated to reflux for 16 hours undervigorous stirring. The mixture was cooled to room temperature andsulphuric acid (588 g) was added. The two phase mixture was heated againunder vigorous stirring. At about 70° C. gas began to evolve. Heatingwas continued until the gas evolution ceased. The reflux condenser wasreplaced by a distillation device which allowed the separation of alower phase while returning the upper phase to the flask. Methanol (150g) was added and the mixture was heated for distillation. Distillationwas carried out at ambient pressure without any intent forrectification. The condensed vapors separated into two phases. The lowerphase was collected and the upper phase was returned to the flask.Distillation was continued until no more lower phase separated from thecondensate. The combined crude ester (493 g) was purified byfractionated distillation, resulting in 401 g CF₃O(CF₂)₃OCHFCOOCH₃ witha boiling point of 51 to 52° C./22 mbar. This corresponds to a yield of78%, based on vinyl ether used. The ester was converted to the ammoniumsalt by heating with aqueous ammonia and removal of methanol byfractionated distillation.

Alternatively, the previous reaction was repeated but 36 g of an aqueoussolution containing 11 g of CF₃O(CF₂)₃OCHFCOONH₄ was used as phasetransfer catalyst instead of methyl trioctyl ammonium chloride. Themixture was slowly heated to 70° C. internal temperature. Total reactiontime was 26 hours. Work up was carried out as described above. 438 g ofdistilled CF₃O(CF₂)₃OCHFCOOCH₃ was received. This corresponds to a yieldof 83% (calculation includes the amount of phase transfer catalyst).

The conversion to the ammonium salt was carried out as above.

Preparation of Compound 13: C₃F₇OCHFCF₂COONH₄

a. Preparation of CF₃CF₂CF₂OCHFCF₂CH₂OH

In a 2 liter glass flask equipped with a stirrer, thermometer, refluxcondenser, and dropping funnel were placed 1008 g methanol, 266 gperfluoropropyl vinyl ether, and 9.2 g of Rongalit® (sodiumhydroxymethyl sulfinate). The reaction mixture was heated to reflux,resulting in an internal temperature of 29° C. 7.1 g t-butylhydroperoxide (70% in water) is added in aliquots during a 9 h timeframe. The internal temperature reached 52° C. at the end. The reactionmixture showed a single liquid phase and some solids. The liquid wasanalyzed by GC and indicated a content of 223 g of C₃F₇OCHFCF₂CH₂OHwhich corresponded to a yield of 75%.

Distillation of the reaction mixture resulted in 171 g of product (bp54° C./23 mbar) corresponding to an isolated yield of 57%.

b. Preparation of C₃F₇OCHFCF₂COONH₄

A 2 liter glass flask equipped with a thermometer, reflux condenser,dropping funnel and stirrer was used. 674 g water, 136 g KMnO₄, and 38 gNaOH are placed in the flask. 169 g C₃F₇OCHFCF₂CH₂OH were added to thewell stirred mixture via the dropping funnel. The temperature is heldbelow 50° C. Residual permanganate was destroyed by addition of a smallamount of methanol. The resulting slurry was filtered to remove theMnO₂. After washing the filter cake with water, the combined filtratewas transferred to a distillation apparatus and acidified with 65 g ofsulfuric acid. 100 g methanol was added and a flash distillation wasstarted. The distillate formed two layers. The lower layer was separatedand the upper layer returned to the distillation pot. In total 182 glower layer were collected. Fractionation of the crude ester resulted in137 g of C₃F₇OCHFCF₂COOCH₃ with a boiling point of 55-56° C./52 mbar.This corresponds to a yield of 77%.

The ester was converted to the ammonium salt by saponification withaqueous ammonia and subsequent removal of methanol by distillation.

Preparation of Compound 11: CF₃O(CF₂)₃OCHFCF₂COONH₄

a. Preparation of CF₃O(CF₂)₃OCHFCF₂CH₂OH

Using equipment similar to the described above, 255 g ofperfluoromethoxypropyl vinyl ether and 730 g methanol were convertedwith Rongalit and t-butylhydroperoxide as radical source. Reactiontemperature started at 47° C. and reached 64° C. at the end. Work up bydistillation yielded 166 g of pure CF₃O(CF₂)₃OCHFCF₂CH₂OH with a boilingpoint of 60-61° C./20 mbar. This corresponds to a yield of 59%.

b. Preparation of CF₃O(CF₂)₃OCHFCF₂COONH₄

A 2 liter glass flask equipped with a thermometer, reflux condenser,dropping funnel and stirrer was used. 159 g of CF₃O(CF₂)₃OCHFCF₂CH₂OH,520 g water, and 100 g sulfuric acid were added to the flask. 190 gKMnO4 were added manually to the liquid over a period of 2 hours whilestirring. The reaction temperature increased to 95° C. over time. Aftera post reaction time of two hours, an aqueous solution of sodiumbisulfite was added until a clear solution was formed. 100 g of methanoland in total 400 g of 50% aqueous sulphuric acid were added. Flashdistillation of the reaction mixture resulted in a two phase distillate.Fractionation of the lower phase (120 g) gave 85.5 g ofCF₃O(CF₂)₃OCHFCF₂COOCH₃ (bp 34-35° C./6 mbar; yield 50%).

The ester was converted to the ammonium salt by saponification withaqueous ammonia and subsequent removal of methanol by distillation.

Preparation of Compound 6

CH₃—O—CF₂—CF₂—COOCH₃ was fluorinated as described in WO 01/46116; theacid fluoride CF₃—O—CF₂—CF₂—COF was then converted into the methylester.The distilled ester was converted into the ammonia-salt as describedabove.

Preparation of Compound 14: CF₃—CFH—O—(CF₂)₅COONH₄

A sample of diacid fluoride, FCOCF(CF₃)—O—(CF₂)₅COF (500 g, 1.1 mol)prepared from the hexafluoropropylene oxide (HFPO) coupling ofperfluoroadipoyl fluoride as described in U.S. Pub. No. US 2004/0116742and was added over 2 hours to a stirred slurry of sodium carbonate (500g, 4.7 mol) in 500 g of diglyme at 85° C. to make the disalt. Thereaction liberated CO₂ gas. Distilled water (25 g, 1.4 mol) was added at85° C. The mixture was heated up to 168° C. with CO₂ off-gassing andheld for 30 minutes. Reaction was cooled down and sulphuric acid (350 g,3.6 mol) in 1100 g of water was added to make the reaction mixtureacidic. Bottom phase was washed with 400 g of 50% sulfuric acid andvacuum distilled to give CF₃—CFH—O—(CF₂)₅COOH 426 g, 1.0 mol for a 95%yield having a boiling point of 132-135° C./15 mm. This was followed bythe addition of 46 g NaOH in 63 g of water. Dried salts in vacuum ovenat 112° C./15 mm Hg to give 386 g of slight yellow sticky solids. To thesalt was added sulphuric acid and the lower fluorochemical phase wasvacuum distilled. The previous process was repeated two more times toyield a colorless acid. The surfactant CF₃—CFH—O—(CF₂)₅COONH₄ having amelting point of 159-165° C. was made quantitatively from the reactionof 200 g of acid reacted with excess ammonium hydroxide and dried.

Preparation of Compound 15: CF₃—CFH—O(CF₂)₃COONH₄

A sample of diacid fluoride, FCOCF(CF₃)—O—(CF₂)₃COF (503 g, 1.4 mol)prepared from the HFPO coupling of perfluorosuccinyl fluoride asdescribed in US Pub. No. 2004/0116742 and was added over 2 hours to astirred slurry of sodium carbonate (387 g, 3.7 mol) in 650 g of diglymeat 78° C. to make the disalt. The reaction liberated CO₂ gas. Distilledwater (35 g, 1.9 mol) was added at 85° C. The mixture was heated up to165° C. with CO₂ off-gassing and held for 30 minutes. Reaction wascooled down and sulphuric acid (250 g, 2.6 mol) in 1250 g of water wasadded to make the reaction mixture acidic. To the bottom phase was added60 g NaOH in 60 g of water. Dried the salt in vacuum oven at 112° C./15mm and recovered 450 g. To the salt was added 300 g of 50% sulphuricacid and the lower fluorochemical phase was washed once with 200 g of50% sulphuric acid. Vacuum distillation gave CF₃—CFH—O—(CF₂)₃COOH (400g, 1.3 mol) for a 95% yield having a boiling point of 111° C./15 mm Hg.The acid was treated with caustic followed by sulphuric acid and vacuumdistilled. This was repeated a second time to yield a colorless acid.The surfactant CF₃—CFH—O—(CF₂)₃COONH₄ having a melting point of 64-68°C. was made quantitatively from the reaction of 208 g of acid reactedwith excess ammonium hydroxide and dried.

Preparation of Compound C-3: C₃F₇—O—CF(CF₃)—CF₂—O—CF₂—COONH₄

Conversion of CF₃CF₂CF₂OCF(CF₃)CF₂OCF═CF₂ toCF₃CF₂CF₂OCF(CF₃)CF₂OCF₂COOCH₃ (bp 91-92° C. at 133 mbar) was carriedout as described in U.S. Pat. No. 4,987,254. The ester was reacted withaqueous ammonia and methanol was removed by distillation resulting inCF₃CF₂CF₂OCF(CF₃)CF₂OCF₂COONH₄. All structures were confirmed by F-NMRspectra. Due to an isomer content in the vinyl ether, an isomer with thestructure CF₃CF₂CF₂OCF₂CF(CF₃)OCF₂COOX (X=CH₃, NH₄) was found.

Preparation of Compound 16: C₃F₇—O—C₂HF₃—O—CH₂—COONH₄

A mixture of 320 ml Tetrahydrofurane, 40 g Hydroxy acetic methylesterand 188 g PPVE is cooled to 0° C., 27 g KOH-powder are added in smallportions—during the addition of KOH, the reaction mixture heats up to60° C. After the addition of KOH, the whole reaction mixture is agitatedfor 6 h at 25° C. The precipitated salt is separated by filtration,dissolved in 300 ml water and then treated with 57 g H₂SO₄ (conc). Theresulting mixture separates in two layers; the lower phase isC₃F₇—O—C₂HF₃—O—CH₂—COOH, 86 g (56%). The distilled acid (bp. 125° C., 20mbar) is neutralized with 25% aqueous ammonia solution to provide a 30%solution in water.

Compounds 2, 3, 4 were prepared from the corresponding carboxylic acids(purchased from Anles Ltd. St. Petersburg, Russia) by neutralizing withaqueous ammonia.

Compounds 7, 8, 10 were prepared from the corresponding carboxylic acidfluorides (˜COF) [purchased from Exfluor, Round Rock, Tex., USA]. Theacid fluorides were converted by addition of methanol to themethylester. The distillated methylester were saponified with aqueousammonia at 60-80° C. and methanol is removed by distillation. CompoundC-2 was prepared as described in U.S. Pat. No. 6,703,520 (column 7).

Determination of Bio-Accumulation

The perfluorinated and partially fluorinated carboxylates were evaluatedfor urinary clearance using a pharmacokinetic study in rats. The goalwas to measure the total amount of parent compound eliminated viaurinary output and estimate the rate of elimination. The study wasapproved by the IACUC (Institutional Animal Care and Use Committees) andwas performed in 3M Company's AAALAC (Association for Assessment andAccreditation of Laboratory Animal Care)-accredited facility.

The study utilized male Sprague Dawley rats, 6 to 8 weeks of age, andapproximately 200 to 250 g body weight at study onset. The testcompounds of table 2 were administered at a dose of 73 micro Moles perkg body weight in rats (N=3 animals per tested compound). All testcompounds were prepared in sterile deionized water and given to rats viaoral gavage. After test compounds administration, the rats were housedindividually in metabolism cages for urine collection: 0 to 6 hours, 6to 24 hours, 24 to 48 hours and 72 to 96 hours. Animals were observedthroughout the study for clinical signs of toxicity. Gross necropsy wasperformed at the termination of each study (96 hours post-dose) withsera and liver samples being retained from each animal.

The concentration of the parent compound or metabolites thereof werequantitatively measured via fluorine NMR on each urine sample for eachanimal at each time point based on internally added standards.

The bioaccumulation data obtained in accordance with the above test arereported in table 2 below.

TABLE 2 Compound- % Recovery related T ½ (h) (96 h) Effects C-1 ~550   6 Hepatomegaly C-2 29 40 Hepatomegaly C-3 95  5 Hepatomegaly Compound 110 73 — Compound 2 12 96 — Compound 3 12 100  — Compound 4 15 50 —Compound 5 11 97 — Compound 6 11 100  — Compound 7 10 100  — Compound 812 82 — Compound 9 31 42 Hepatomegaly Compound 10 10 99 — Compound 11 1284 — Compound 12 11 95 Compound 13 11 94 — Compound 14 24 32Hepatomegaly Compound 15  8 95 — Compound 16  13*  65* — *No parentcompound observed in the urine. T ½ and % recovery are based onelimination of the major metabolite—C₃F₇—O—CHFCOO⁻. T_(1/2) is the timerequired for the amount of a particular substance in a biological systemto be reduced by one half by biological processes when the rate ofremoval is approximately exponential. In these examples the value ofT_(1/2) is calculated by exponential least squares curve fitting (y =Ae^(Bx) and T_(1/2) = 0.693/B) where y represents the concentration ofanalyte in urine and x represents time in hours.

TABLE 3 2 (140 C-1 C-2 C-3 1 mmol) 3 4 5 6 Polymerization 101 77 87 74109 69 82 73 84 time (min) Average Particle 111 118 113 110 129 115 109122 122 Size (nm) SSG 2.166 2.165 2.149 2.169 2.157 2.165 2.163 2.1692.175 (g/cm³) Solid content 9.9 10.0 10.3 10.3 9.7 10.1 10.2 10.0 7.1(w-%) 7 14 (140 (140 mmol) 8 9 10 11 12 13 mmol) 15 Polymerization 73 7972 72 82 82 83 75 78 time (min) Average Particle 129 115 113 102 126 108128 127 105 Size (nm) SSG 2.159 2.167 2.165 2.166 2.168 2.167 2.1642.151 2.154 (g/cm³) Solid content 10.1 10.0 10.2 10.1 10.2 10.3 10.2 8.110. (w-%)

Example 1 A PTFE-Dispersion was Prepared According to the FollowingPolymerization Process

The polymerization was performed in a 40 l kettle equipped with animpeller agitator and a baffle. The kettle was charged with 30 l ofdeionized water and set to 35° C.; the kettle was evacuated repeatedlyto remove oxygen; Agitation speed was set to 165 rpm. The oxygen freekettle was charged with 70 mmol of ammonium 2,4,6trioxa-perfluoro-octanoate (called in the following “fluorinatedemulsifier”) (CF₃—(OCF₂)₃—COONH₄) and the following materials wereadded: 0.5 ml of a solution containing 40 mg of copper sulphate pentahydrate and 1 mg of conc. sulphuric acid; 15 g of a 25 w-% of aqueousammonia solution and 5.6 g of CF₃CF₂CF₂OCF(CF₃)—CF₂—O—CF═CF₂ (PPVE-2).Finally the reactor was pressurized with tetrafluoroethylene (TFE) to0.2 MPa and 47 g of hexafluoropropylene (HFP) were added. The kettle wasthen set to 1.5 MPa using TFE and 100 ml of an aqueous initiatorsolution containing 140 mg of sodium disulfite followed by 100 ml of asolution containing 340 mg of ammonium peroxodisulfate was pumped intothe reactor. The beginning of the polymerization is indicated by apressure drop. During polymerization the pressure was maintained at 1.5MPa by feeding TFE continuously. After 3.2 kg of TFE had been added, themonomer valve was closed and the pressure was released.

The so obtained polymer dispersion had a solid content of 10.1 wt-% anda pH of 9.6. The latex particle diameter was 115 nm according to dynamiclight scattering. Before removing the fluorinated emulsifier by an ionexchange process, 8% (based on solids content) of Genapol X 080(non-ionic emulsifier) were added to the dispersion. The fluorinatedemulsifier was measured to be 700 ppm before ion exchange.

A commercially available strong basic ion exchange resin AmberliteIRA402 Cl (capacity 1.3 mol/l) was used to remove the fluorinatedemulsifier. The column was filled with 300 ml anion exchange resin andbrought into OH-form by passing 12 bed volumes (BV) (1BV is equal to 300ml) of NaOH (4% in water) through the column (flow rate 3 BV/h). Theresin was washed with 10 BV deionized water and 3 BV of Genapol X 080(1% in water). The Dispersion was then passed through the ion exchangecolumn from bottom to top. Flow rate varied between 0.5 to 1.5 BV/h.

After different amounts of dispersion had passed through the ionexchange column (see table 4) a sample was taken and the residualfluorinated emulsifier content was measured. No clogging of the columnwas observed. The solid content of the dispersion and the averageparticle size of the latex after removal of fluorinated emulsifierremained unchanged. The pH of the dispersion after ion exchange wasabout 10.6.

TABLE 4 Amount of Dispersion Residual Fluorinated passed through columnEmulsifier content in Sample (BV) Disperison (ppm) 1 5 <10 ppm 2 17 <10ppm 3 35 <10 ppm 4 62 <10 ppm

Example 2

A PTFE dispersion with a solid content of 21 wt-% and a particle size of220 nm containing about 900 ppm of the fluorinated emulsifier ammonium2,4,6,8 tetraoxa-perfluoro-decanoate (CF₃—(OCF₂)₄—COONH₄) was ionexchanged in the presence of 5% of Triton™ X 100 (based on solidscontent). The pH of the dispersion before ion exchange was pH=8.8 andafter ion exchange about 10.5. The ion exchange resin was preparedaccording to Example 1, except for washing the resin with Triton™ X 100(1% in water) instead of Genapol™ X 080. The residual fluorinatedemulsifier content is given in table 5. The solid content of thedispersion and the average particle size of the latex after removal offluorinated emulsifier remained unchanged. No clogging of the column wasobserved.

TABLE 5 Amount of Dispersion Residual Fluorinated passed through columnEmulsifier content in Sample (BV) Disperison (ppm) 1 6 <10 ppm 2 12 <10ppm 3 19 <10 ppm 4 25 <10 ppm

After ion exchange the dispersion was thermally up concentrated to asolid content of 58%. Prior to up-concentration, 1000 ppm of anionicsurfactant Hostapur™ SAS 30 was added.

What is claimed is:
 1. Method comprising: (i) providing a fluoropolymer dispersion comprising fluoropolymer particles and one or more fluorinated surfactants selected from fluorinated carboxylic acids or salts thereof having the general formula: [R_(f)—O-L-COO⁻]_(i)X^(i+)  (I) wherein L represents a linear fully fluorinated alkylene group, R_(f) represents a linear fully fluorinated aliphatic group or a linear fully fluorinated aliphatic group interrupted with one or two oxygen atoms, X^(i+) represents a cation having the valence i and i is 1, 2 or 3, wherein the fluorinated carboxylic acids or salts thereof have no more than 3 carbon atoms sequentially bonded; (ii) adding one or more non-fluorinated surfactants selected from anionic and non-ionic surfactants; and (iii) reducing the total amount of said one or more fluorinated surfactants to an amount of not more than 500 ppm based on the total weight of the dispersion while maintaining or increasing the amount of solids in the dispersion.
 2. Method according to claim 1 wherein said one or more non-fluorinated surfactants consist of non-ionic surfactants and wherein the amount of said fluorinated surfactants is reduced by contacting the fluoropolymer dispersion with an anion-exchange resin.
 3. Method according to claim 1 wherein the amount of said fluorinated surfactants is reduced by ultrafiltration or by steam distilling the fluorinated surfactant in its free acid form.
 4. Method according to claim 1 wherein said fluoropolymer dispersion comprises non-melt processible tetrafluoroethylene homo- or copolymer.
 5. Method according to claim 1 wherein the method further comprises concentrating the fluoropolymer dispersion.
 6. Method according to claim 1 wherein at least one non-ionic and at least one anionic non-fluorinated surfactant are added to the dispersion, at least one of said non-ionic and anionic non-fluorinated surfactant being added to the dispersion prior to reducing the amount of fluorinated surfactant in the dispersion.
 7. Method according to claim 1 wherein said non-ionic non-fluorinated surfactants are selected from non-aromatic surfactants.
 8. Method according to claim 1 wherein said non-ionic non-fluorinated surfactants are selected from surfactants of the general formula: R¹—O—[CH₂CH₂O]_(n)—[R²O]_(m)—R³  (XV) wherein R¹ represents an aromatic or aliphatic hydrocarbon group having at least 8 carbon atoms, R² represents an alkylene having 3 carbon atoms, R³ represents hydrogen or a C₁-C₃ alkyl group, n has a value of 0 to 40, m has a value of 0 to 40 and the sum of n+m being at least
 2. 9. Method according to claim 1 wherein said anionic non-fluorinated surfactant is selected from surfactants having a carboxylic acid group or salt thereof and an aromatic or aliphatic hydrocarbon group.
 10. A method according to claim 1 wherein the anion of said fluorinated carboxylic acids or salts thereof have a molecular weight of not more than 1000 g/mol.
 11. A method according to claim 1 wherein the anion of said fluorinated carboxylic acids or salts thereof have a molecular weight of not more than 500 g/mol.
 12. A method according to claim 1 wherein the fluorinated carboxylic acid or salt thereof when administered to rat shows a renal recovery rate of at least 50% of the administered amount, 96 hours after administration and wherein the renal half-life (T_(1/2)) is not more than 30 hours.
 13. A method according to claim 1 wherein the fluorinated carboxylic acid or salts are selected from fluorinated carboxylic acid or salts of which any fluorinated aliphatic portion has not more than 3 carbon atoms.
 14. A method according to claim 1 wherein L in said formula (I) is selected from the group consisting of linear perfluorinated alkylene groups having 1 to 3 carbon atoms.
 15. A method according to claim 1 wherein R_(f) is selected from the group consisting of linear perfluorinated aliphatic groups having 1 to 3 carbon atoms or linear perfluorinated aliphatic groups interrupted with one or two oxygen atoms of which alkylene groups between oxygen atoms have not more than 3-carbon atoms and wherein the terminal alkyl group has not more than 3 carbon atoms.
 16. A method according to claim 1 wherein L is selected from the group consisting of —(CF₂)_(g)— wherein g is 1, 2, or
 3. 17. A method according to claim 1 wherein R_(f) corresponds to one of the following formulas: (i) R_(f) ¹—[OR_(f) ²]_(p)—[OR_(f) ³]_(q)—  (II) wherein R_(f) ¹ is a perfluorinated linear aliphatic group of 1 to 3 carbon atoms, R_(f) ² and R_(f) ³ each independently represents a linear perfluorinated alkylene of 1, 2, or 3 carbon atoms and p and q each independently represent a value of 0 to 1 and wherein the sum of p and q is at least 1; (iii) R_(f) ⁸—(OCF₂)_(a)—  (IV) wherein a is 1 and R_(f) ⁸ is a linear fully fluorinated aliphatic group having 1, 2, or 3 carbon atoms; and (iv) R_(f) ⁹—O—(CF₂)_(b)—  (V) wherein b is an integer of 1 to 3, and R_(f) ⁹ is a linear fully fluorinated aliphatic group having 1, 2, or 3 carbon atoms.
 18. A method according to claim 1 wherein the fluorinated carboxylic acid corresponds to one of the following formulas: (i) R_(f) ^(c)—(OCF₂)_(u)—O—(CF₂)_(v)-AC  (VIII) wherein u is 1, v is an integer of 1 to 3, R_(f) ^(c) represents a linear perfluorinated aliphatic group of 1, 2, or 3 carbon atoms and AC represents a carboxylic acid group or salt thereof; and (ii) R_(f) ^(c)—O—(CF₂)_(y)—O-L¹-AC  (IX) wherein y has a value of 1, 2, or 3, L¹ represents a linear perfluorinated alkylene of 1, 2, or 3 carbon atoms, R_(f) ^(c) is as defined in above formula (VIII) and AC represents a carboxylic acid group or salt thereof.
 19. A method according to claim 1 wherein the fluorinated carboxylic acid or salt thereof is selected from the group consisting of CF₃—O—CF₂—CF₂—COOH C₂F₅—O—CF₂—CF₂—COOH C₃F₇—O—CF₂—CF₂—COOH CF₃—(O—CF₂)₂—O—CF₂—COOH CF₃—(O—CF₂)₁—O—CF₂—COOH CF₃—(O—CF₂—CF₂)₁—O—CF₂—COOH C₂F₅—(O—CF₂—CF₂)₁—O—CF₂—COOH C₂F₅—(O—CF₂—CF₂)₂—O—CF₂—COOH CF₃—(O—CF₂—CF₂)₂—O—CF₂—COOH C₃F₇—O—CF₂—COOH CF₃—O—CF₂—CF₂—CF₂—O—CF₂—COOH CF₃—CF₂—O—(CF₂)₃COOH CF₃—CF₂—O—(CF₂)₅COOH and salts of any of these fluorinated carboxylic acids.
 20. A method according to claim 1 wherein the total amount of said one or more fluorinated surfactants is reduced to an amount of not more than 250 ppm. 